In the hard copy technology, thermal transfer recording having the properties such as non-impact, ease of operation and maintenance, and the probabilities of cost reduction and miniaturization, etc. attracts attention as a recording method. In a thermal transfer recording system, in printing, a transfer sheet (ink ribbon) having an ink layer serving as a colorant-containing layer is superposed on a receiving sheet, and a colorant-containing component or a colorant is transferred as fine dots onto the receiving sheet by melting or sublimation under heating by a thermal head from the ink ribbon side.
As a substrate of the receiving sheet for such thermal transfer recording, a white polyester film comprising polyester containing inorganic fine particles of titanium oxide, calcium carbonate, barium sulfate, or the like, or a resin noncompatible with polyester is conventionally used.
In general, such a film comprises a receiving layer provided thereon for improving a printing function, and is used as the receiving sheet for thermal transfer recording. However, there is demand for a white polyester film having high whiteness, permitting improvements in the accuracy of recording and the clearness of a printed image, and providing a feel of high grade.
In order to comply with this demand, films containing plural types of the above-described inorganic fine particles, films containing both the inorganic fine particles and a noncompatible resin, etc. are proposed in, for example, Japanese Unexamined Patent Application Publication Nos. 4-153232, 6-322153, etc.